Attenuator for ultra high frequencies



Oct. 12, 1948. s, c, CLARK, JR 2,451,201

ATTENUATOR FOR ULTRA HIGH FREQUENCIES Filed April 15, 1944 /0 /4 h p gl. l 2 a INSULATION Inventor: Stephen OCIark JR,

Hi s Attorney.

Patented 12, 1948 ATTENUATOR FOR ULTRA HIGH FREQUENCIES Stephen C. Clark, Jr., Scotia, N. Y., assignor to General Electric fiompany, a corporation of New York Application April 15, 1944, Serial No. 531,224

8 Claims. 1

My invention relates to ultra high frequency systems, and more particularly to an attenuator for utilization therein. In such systems, the problem frequently arises of connecting a utilization circuit, for example a frequency determining meter, to an input circuit in which the intensity of the incident wave may vary over a considerable range. Moreover, since in such systems it is desirable to have impedance matching throughout, any attenuator for varying the intensity of an ultra high frequency wave transmitted to a utilization device should provide a minimum discontinuity in the system, so that no reactive effect of consequence is transferred to either the input or the utilization circuits. Accordingly, it is an object of my invention to provide a new and improved attenuator for ultra high frequency systems in which reactive effect on circuits coupled thereto is minimized.

t is another object of my invention to provide a new and improved attenuator for systems of this nature wherein accurately controllable and determinable amounts of attenuation may be obtained.

It is a further object of my invention to provide a new and improved attenuator for an ultra high frequency system which comprises a concentric transmission line connected between the input and output circuits of the system, which transmission line includes a variable capacitance element for attenuating the ultra high frequency waves transmitted between the circuits.

Briefly stated, in accordance with the illustrated embodiments of my invention, I provide in an ultra high frequency system a concentric transmission line along which an ultra high frequency electromagnetic wave is propagated and in which a variable capacitance is serially connected between adjacent sections of one of the conductors of the line. The variable capacitance includes an insulator connected between sections of the inner conductor and a metallic sleeve slidable along one of the sections and over an adjustable portion of the insulator. The Variable capacitance is of such size that, in comparison with the input and output shunt capacitances of the adjacent sections of the concentric transmission line, the effect of its variation on the input and output impedances, and hence on the circuits connected to the line, is negligible.

For a better understanding of 'my invention, reference may be had to the following descrip tion taken in connection with the accompanying drawing and its'scope will be pointed out in the appended claims, Fig. 1 is a longitudinal crosssectional view of one embodiment of my invention including the attenuator connected in a concentric transmission line, and Fig. 2 is a vertical cross-sectional view along the lines 2-2 of Fig. 1. Fig. 3 represents a modification of the attenuator of my invention as embodied in a concentric transmission line and which employs means for more accurately controlling and determining the amount of attenuation, and Fig. 4 is a vertical cross-sectional View of the attenuator of Fig. 3 taken along the lines 44.

Referring to Figs. 1 and 2 jointly, there is shown an attenuator which comprises a section of concentric transmission line having a tubular outer conductor I and a centrally disposed inner conductor 2 along which an ultra high frequency electromagnetic wave is propagated. The centrally disposed inner conductor comprises two similar metallic sections 3, 4 which are separated by a spacer 5 of any suitable insulating material, such as, for example, polystyrene. The sections 3 and 4 at their adjacent ends are provided with portions of reduced diameter 6 which fit in cooperating holes in the ends of spacer 5. The spacer 5 and the sections 3, 4 are all of the same diameter so that physically the inner conductor 2 appears as a continuous cylindrical member which is supported within the outer conductor l by means of a plurality of insulators 1.

Supported on the inner conductor 2 is a dielectric cylinder 8 of any suitable insulating material, such as, for example, polystyrene. The dielectric member 8 has a central bore into which is fitted a conductive member in the form of a metallic sleeve 9, the sleeve being spun over at the ends of the dielectric cylinder to form a rigid construction. The sleeve 9 has an inner diameter which is substantially equal to the outer diameter of the section 3 and is in contact with this section of the inner conductor and transmission line. The metallic sleeve 9, moreover, extends over a portion of the insulating spacer 5. The dielectric cylinder 8 is provided at its left-hand end with a. protruding portion to which extends through a slot or an opening it in the outer conductor l. The protruding portion lo moreover is provided with threads which engage threads within a metallic sleeve I 2 which surrounds the outer conductor I adjacent the slot H.

In construction, the outer conductor may be formed in a plurality of parts, such as a pair of end sections [3, l4 and an intermediate section l5, the intermediate section containing the slot H. The section 33 may be joined to the section I5 by means of a plurality of screws I6, while the section 14 may contain a shoulder l1 against which is abutted an internally threaded nut l8 and which may be used for connecting the lefthand portion of the transmission line to an input circuit. The intermediate section I has a shoulder portion I9 adjacent the slot II and the threaded sleeve l2 abuts against this shoulder. A collar '20 abutting against the gopposite end of sleeve 12 prevents-longitudinal motion of the sleeve on the intermediate section 15, while per-. mitting rotation of the sleeve about this portion of the outer conductor.

In operation, the left-hand portion of the. concentric transmission line may be .connectedto an input circuit, such as a source -ofultra'high iflequency electromagnetic waves, while the righthand portion of the attenuator comprising the section 4 of the inner conductonandcthesection l3 oi the outer conductor may be connected to a load circuit such as, for example, a frequency determining meter (not shown) Insuch *ul-trahigh frequencyapplications;- of course,- it

isicustom-ary to have the impedance ofithe conne'ctingytransmissim lines match with the impedances of such a source and-such a load. .1". This impedance includes the relatively ;high-,' shunt capacitance incident to theposition of the inner conductor within the :outei" conductor of the transmission :line. Since. in some applications itis desirable-to have the voltage supplied to a load circuit maintainedconstant while the voltage from an i put circuit may. vary over a considerable range; attenuation of theultra'high irequencyinputwave is required." In the constructionj above described, the .opposed. ends of condoctors". 31 and" 4. separated by the insulating spacer 5; form a capacitance of small value which is connected in series with the sections 3," G of the inner conductor yoi the transmissionglineand which" attenuates the; high frequency Wave traveling along that. line: The conductive, member or. sleeve 9" forms. means for. varying' the value of this capacitance. ThisVariation is obtainedzby rotation'of' the sleevejl2 to move'the "dielectriccylinder 8 and; thejsleeve. 9 along the spacer. 5,-the movement providing a. continuous variation. of the, attenuation of" the high frequency; wave;";This seriesicapacitance, moreover, is relatively smallcompared to the shunt capacitance which exists between the inner andouter c d ct s 2130f the transmission. line., Accordingly, substantially nov reactive. .efiect .onanyload circuit which may .be connected -between.-. members and" i3 is obtained, the. input, and .output impedances being. maintained constant. as. the

attenuation is varied over, a .substantialrange,

for example, from a fewde'cibels to analmostinfinite amount of attenuation.

In the modifications of .the invention illustrated irrFigs, 3 and 4, a precisionattenuator isshown which has no protruding surface,.,-but instead the rack 25 is formed,on..one surface. Also the position of insulating spacer Erelative touthe inputand. output .ends'of the attenuator is reversed from that shown in the structure in Fig. 1.. Thus,

the member 5 is. positionedbetweenzsleeve 8 and the input conductor 3and,.in.the,v minimum attenuation position shown in. Fig. 3,.lies- .almost entirely within dielectric sleeve, 8. The rackdi is engaged by a pinionL2Z. which is supported in a. bearing structure comprising. ahousing-portion 23 whichis attachedto. the outer. conductor sectionv l5and a faceplate 24. which. is fastened to the housing member by means of a plurality ofyscrewsiii. A gasket1:26,..interposedbetween the face plate 24 and the housing member 23, can make the structure water-tight. The pinion 22 may .be rotated by a control knob 21 which carries a pointer 28 and cooperates with a scale 5 29 on the face plate to indicate precisely the amount of attenuation obtained.

From the foregoing, itis seen that my invenwtion provides avariable attenuator! for an ultra high frequency wave which is simple in con struction and operation and which produces a continuously variable amount of attenuation ywhichhasno appreciable effect on the load cir- ..-'G.U.ltS connected thereto.

While I have shown a particular embodiment 'of.1ny .invention, it will of course be understood that I do not. wish to be limited thereto since various modifications may be made, and I contemplateby the-appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What. I claim as new and: desire to secure by fLettersPatent of the United States is:

1. .An. attenuator for a high frequency-electromagnetic- .wave comprising a transmission line .having a pair. of -conductors, oneof said conduc- .tors. being continuous in character, the -other oi -saidconductors. consisting-of two sections separated by aninsulating spacer, the; opposed ends ofnsaid sections. and .said. spacer constituting a -.capacitance..connecting said sections. and pro- ..viding attenuation. of-said Wave; andafconduc- .tive member ,movable 1 along said; spacer -.to vary ,said... capacitancev andv the amount -ofasaidattenuation.

2..An.attenuato1 .-ior an ultra=higlr frequency electromagnetic wave comprising a. concentric transmission line constitutedby a tubular outer conductorgand. a centr-allydisposed inner con= ductor, said inner conductonconsisti-ngof-two sections separated; by I an insulating spacenethe opposedendsofsaid-sections and said spacercon- .stituting a capacitanceconnecting, said sections and providing attenuation on said wave; and a conductive sleeve slidable along said spacerpto vary. said capacitance.- and: the.- amount of :said attenuation.

- .3. Invanattenuatorfor ultrahigh frequency .wave,.the combination oi a section-of:concentric transmission line comprising atubulanoutenconductor. and a-.c.entrally. disposed inner conductor, .said. inner conductor consistin of twolongitudinally spaced sections connected by. av cylindrical insulator, aemetalhc sleeve .con-tactingone of .said sections. and .s-lidablealong said insulator, ,andnmeans ion, adjustingwthe; position ;of; said sleeve v on .said insulator.

. 4. 1n combination a concentric:transmission line. along which. an ultra high frequencyielec- .tromagnetic wave-is: propa ated, .said; transmis- .sion 1ine (having an inner conductor comprising two conductivesectionswseparated by a. non 5conductive. section; comprising a .-solid-dielectricwmaterial, thegopposed-t ends of said conductive sec- .tions-,- and saidenon-conductive :SfiClilDll constituting-a capacitance connecting said sections; and providing...attenuation; oil-said. -wave,-'; andzmeans forcontinuously yarying. the-.amountr oiasaid cat- .tenuation, saidi means. comprising a conductive sleeve. connected to .one:.ofsaidsconductivezsecconductive -section.

. 5.. At. attenuatonforan ultra. highfrequency electromagnetic wave. comprising a:- concentric transmission. dine. having autubulari .outer conductor and. aecentrally; disposed .inner...c.onductor,

tions and. adjustable in position: along-asaid gnonsaid inner conductor consisting of two conductive sections having their adjacent ends in opposed spaced relation to form a capacitance conmeeting said sections and providing attenuation of said waves, solid dielectric means positioned between said ends and forming a spacer therebetween, and means for varying the amount of said attenuation, said last means comprising a conductive member connected to one of said sections and adjustable in position relative to the 'end of the other of said sections.

6. In combination, a concentric transmission line along which a high frequency electromagnetic wave is propagated, said line comprising a tubular outer conductor and a centrally disposed inner conductor, one of said conductors comprising a pair of sections having adjacent ends in opposed spaced relation to provide a capacitance connecting said sections for attenuating said wave, solid dielectric means positioned between said ends and forming a spacer therebetween, and means for varying the amount of said attenuation comprising a conductive member connected to said one section and variable in position relative to the other of said sections.

7. In an attenuator for a high frequency electromagnetic Wave, the combination of a concentric transmission line comprising a tubular outer conductor and a centrally disposed inner conductor, said inner conductor consisting of a pair of metallic sections connected by a non-conducting section to form a capacitance connecting said metallic sections for attenuating said Wave, and means to vary the amount of said attenuation comprising an insulator surrounding one of said conductive sections and a portion of said nonducting section, said insulator having a conductive surface contacting said conductive sections and said non-conducting section and extending along said non-conducting section and being movable along said inner conductor to vary the value of said capacitance.

8. An attenuator comprising a concentric transmission line and consisting of a tubular outer conductor and a centrally disposed inner conductor, said inner conductor consisting of two sections separated by an insulating spacer, an insulator supported on said inner conductor, said insulator having a conductive sleeve extending along said inner conductor, said sleeve contacting one of said sections and being adjustable in position along said spacer.

STEPHEN C. CLARK, JR.

REFERENCES CITED The following references are of record in the 

